This invention relates to a pipe joining structure wherein multiple pipes or tubes are joined by means of a joining cylinder formed either directly on one of the pipes or on a separate lug.
In the past, when it has been necessary to join a number of tubes or pipes at locations where great strength is required, gas or electric welding has been commonly used to form the joining structure. For example, on a bicycle frame or other similar structure, when an end of one pipe was to be joined at a specified angle to either the center or the end of a second pipe, as shown in FIG. 6, the second pipe B was joined to the first pipe A by first mounting a lug C onto the first pipe A, and then welding this lug C and the pipe A at both edges 1a and 1b of the mounting pipe part 1 of the lug. The second pipe B was then inserted into the joining cylinder 2 formed in the lug C, and the lug C and the second pipe B were welded at the edge 2a' of the pipe insertion end of the joining cylinder 2 formed in the lug C.
In recent years, there have been developed both new materials and composite structures in which these new materials are combined with each other or with conventional materials in order to utilize the characteristics of each of the materials. Because these new materials and the composite structures are both lightweight and strong, demand for them has grown rapidly in fields where lighter weight is needed, and they have come to be widely used as materials for pipes.
However, because these composite structures have composite properties, the joining methods which can be used to connect them are limited. For example, when using a composite structure such as carbon fiber reinforced plastic laminated to the external periphery of aluminum pipe, for the pipes of a bicycle frame, because one of the materials (in this case the carbon fiber reinforced plastic used in the external layer) is easily affected by high temperatures, the conventional method of gas welding cannot be used to form the joints.
It is a general object of this invention to provide a pipe joining structure which enables a strong joint to be formed regardless of the materials used.